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A 40-year-old woman presented to the emergency room with intermittent fever, cough, haemoptysis and dyspnoea for one week. She also had a history of episodic breathlessness with wheezing for the last 5 years. She did not drink alcohol or smoke tobacco, denied intravenous drug abuse or use of steroids. On physical examination, the patient was febrile (temperature, 38.5°C), tachypnoeic and tachycardic. Blood pressure was 150/90 mmHg. Examination of lungs revealed bilateral coarse crackles and rhonchi. The rest of the systemic examination including cardiovascular system was normal. Serial chest X-rays are shown in figures 1 to 3.
- What are the findings on serial chest X-ray ?
- What is the differential diagnosis ?
The first chest X-ray (figure 1), which was taken at presentation, shows bilateral non-homogenous opacities and a thick walled cavity in the left mid-zone with surrounding consolidation. The second X-ray (figure 2), taken a week later, shows bilateral, multiple lung cavitation with air–fluid levels. Pulmonary cavities in both upper and lower lobes are also seen on lateral view (figure 3). The chest X-ray in figure 4, taken approximately 4 weeks after starting treatment, shows significant resolution of pulmonary lesions with antibiotic therapy.
The differential diagnosis of cavitating lesion in lung is given in the box. Inflammatory lesions are the most common cause of lung cavities. The number of cavities may vary from one to many. If the lesion is single, abscess from necrotising Gram-negative or staphylococcal pneumonia should be the first consideration, especially if patient is acutely ill with a severe pneumonia that cavitates.
If multiple cavities are present, the infection is likely due to haematogenous dissemination (septic emboli), and a source for this dissemination should be sought. The source could be right-sided endocarditis or infected venous thrombi.
Tubercular cavities are usually located in the upper zone, either the posterior segment of the upper lobe or apical segment of lower lobe. Because of the high concentration of tuberculous bacilli in the cavity, patients usually have a smear strongly positive for acid-fast bacilli. Lung abscesses secondary to aspiration are frequently right-sided and most often involve the lower zone. Most patients with anaerobic lung abscess would have risk factors for aspiration such as poor dental hygiene, seizure disorder, alcoholic blackouts, etc. The manifestation is often indolent, with complaints of cough, fever, and malaise lasting for weeks to months. A variety of fungi may cause cavitary lesions.Aspergillus, Mucor, andCandida spp rarely cause severe disease in patients without neutropenia. The endemic fungi (histoplasma, blastomyces, and coccidiodes), however, may cause cavitary lesions in immunocompetent hosts. These organisms should be considered in the differential diagnosis of a cavitary lesion if travel to an endemic area has occurred.
Pulmonary lesions due to infected bullae/cysts are thin-walled cavities with smooth outline. Cavitation may rarely complicate pulmonary embolism with infarct, which are usually seen in the lower zone. Thick-walled cavities may result from pulmonary vasculitis, of which Wegener's granulomatosis is the prototype. Wegener's granulomatosis often results in bilateral multiple cavitary lesions, single lesion being less common. Neoplasia, either primary (bronchogenic carcinoma, lymphoma) or metastatic (from squamous cell) involving the lung, also may cavitate. These are usually thick walled and fluid level is seen more commonly with primary tumours than with metastasis.
Differential diagnosis of cavitation on chest X-ray
cavitating pneumonia: S aureus, Gram-negative bacilli (Klebsiella, Pseudomonas, Legionella), anaerobes, mycobacteria, fungi, pneumocystis
septic emboli, bacterial or fungal
Wegener's granulomatosis or pulmonary vasculitis
infected bullae or cysts
neoplasia: primary or secondary
Initial laboratory work-up revealed normocytic anaemia, leucocytosis with shift to left and toxic granulation. Arterial blood gas analysis showed mild hypoxaemia which improved with oxygen therapy. Blood biochemical laboratory values were normal. Sputum Gram stain showed Gram-positive cocci in clusters and culture grewStaphylococcus aureus (methicillin sensitive) on four occasions. Sputum smears and cultures were negative for acid-fast bacilli. Repeated blood cultures did not grow any organisms. Echocardiogram did not show any abnormalities.
The patient was treated with antibiotics, initially with cefotaxime/amikacin, later changed to cloxacillin. She became afebrile after 2 weeks of therapy, but antibiotics were continued for 6 weeks to promote cure. In addition, chest physiotherapy was helpful in drainage of the lung abscess.
Staphylococcal pneumonia is an uncommon, but serious infection. Despite appropriate antibiotic treatment, mortality in staphylococcal pneumonia remains high.1-3 Staphylococcal pulmonary infections are typically nosocomial and usually occur in older adults (sixth decade or older) with concomitant medical illnesses.1 Watanakunakorn3 reported the cases of 44 patients with bacteraemic S aureus pneumonia (positive sputum and blood culture). All patients had at least one underlying condition (intravenous drug abusers were excluded from the study). Virtually all patients in a study by Kaye et al 1 had some underlying illness, particularly chronic pulmonary disease. Our patient was relatively younger, however she did have a history of chronic pulmonary airway disease.
No single radiological presentation is diagnostic ofS aureus pneumonia. However, multiple cavitation or pneumatoceles are characteristically seen, particularly in children and intravenous drug abusers. These cavities are usually thin walled (2–4 mm) and are slightly indistinct on their outer border. Abscess formation has been reported in 23–70% of adult patients presenting with S aureus pulmonary infections.4-6 However, in recent studies,1 2 abscess formation was seen in 16–20% of patients and multiple abscesses occurred infrequently. In the study by Kaye et al 1 all patients had single abscesses. The chest X-rays in these patients typically show multilobar infiltrates, predominantly in the lower lobes, and often bilateral.1 5 6 The frequency of pleural involvement is variable, with estimates ranging from 5% to 48%.1 5 6Our patient had bilateral involvement on presentation and went on to develop multiple abscesses, however, she did not have pleural involvement.
Despite the availability of effective antibiotics, mortality continues to be 30–32%.1 2 This may reflect the fact that patients with S aureus pneumonia tend to be elderly and have other significant illnesses. Treatment is with a penicillinase-resistant penicillin such as naficillin, cefazolin or vancomycin (penicillin allergic or methicillin-resistantS aureus), and 4–6 weeks of therapy is required to promote cure.
Multiple staphylococcal lung abscesses.
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